1. Field of the Invention
The present invention concerns a peptide that causes a marked suppression in protein synthesis. More particularly, the present invention concerns a translation inhibiting peptide obtained from canine cardiac tissue.
2. Background Information
A fundamental question concerning initiation of cardiac hypertrophy is: how can energy be diverted to start the process when the heart itself must function more vigorously? In established hypertrophy, many adaptive factors such as reduced ATPase activity (R. Z. Litten, B. J. Martin, R. B. Low and N. R. Alpert, "Altered Myosin Isozyme Patterns form Pressure-overloaded and Thyrotoxic Hypertrophied Rabbit Hearts", Cir. Res., 50, 856-863, (1982)) and shifts in LDH (G. L. Hammond, B. Nadal-Ginard, N. S. Talner and C. L. Market, "Myocardial LDH Isozyme Distribution in the Ischemic and Hypoxic Heart", Circulation, 53, 637-643, (1976)), CPK (J. S. Ingwall, M. F. Kramer, M. A. Fifer, B. H. Lorell, R. Shemin W. Grossman and P. D. Allen, "The Creatine Kinase System in Normal and Diseased Human Myocardium", N. Engl. J. Med., 313, 1050-1054, (1985)) and possibly myosin isozyme patterns (T. Wisenbaugh, P. Allen, G. Cooper, H. Holzgrefe, G. Beller and B. Carabello, "Contractile Function, Myosin ATPase Activity and Isozymes in the Hypertrophied Pig Left Ventricle after a Progressive Pressure Overload", Circ. Resl, 53, 52-62, (1983); J-J. Mercadier, P. Bouveret, L. Gorza, S. Schiaffino, W. A. Clark, R. Zak, B. Swynghedauw and K. Schwartz, "Myosin Isoenzymes in Normal and Hypertrophied Human Ventricular Myocardium", Circ. Res., 53, 52-62, (1983)) permit anaerobic energy delivery and increased economy of isometric force development (N. R. Alpert and L. A. Mulieri, "Increased Myothermal Economy of Isometric Force Generation in Compensated Cardiac Hypertrophy Induced by Pulmonary Artery Constriction in the Rabbit", Cir. Res., 40, 491-500, (1982)) so that the heart can function more efficiently given the constraints imposed by the chronic stress. In acute cardiac stress, however, such as that produced by sudden aortic banding, the heart still must generate increased contractile force during the time necessary for adaptation, but in the absence of these adaptive measures.
In order to meet the dual requirements of increased contractile force and the initiation of hypertrophy, the acutely stressed cardiac cell saves energy by temporarily throttling down or turning off other non-imminently essential cell functions. Although the end result of hypertrophy is increased protein synthesis, it has been previously reported that one of the earliest responses of cardiac cells to acute stress, imposed either by heat shock or aortic banding, was suppression of protein synthesis caused, at least in part,by translational inhibition, (Y. K. Lai, P. A. Havre and G. L. Hammond, "Cardiac Hypertrophy Cannot Proceed Without Initial Suppression of Protein Synthesis", Biochem. Biophys. Res. Comm., 135, 857-863, (1986)).
Heretofore it has been noted that the aforementioned suppression was associated with a shift in the polysome profile towards the monosome region, (Y-K. Lai, P. A. Havre and G. L. Hammond, "Heat Shock Stress Initiates Simultaneous Transcriptional and Translational Changes in the Dog Heart", Biochem. Biophys. Res. Comm., 134, 166-171, (1986)). As has been previously shown, both stresses share in common a discrepancy between energy requirements and expenditure resulting in similar immediate changes in cell biochemistry, (G. L. Hammond, Y-K. Lai and C. L. Markert, "Diverse Forms of Stress Lead to New Patterns of Gene Expression Through a Common and Essential Metabolic Pathway", Proc. Natl. Acad. Sci., 79, 3485-3488, (1982)).
G. L. Hammond, Y-K. Lai and C. L. Markert, "Preliminary Characterization of Molecules that Increase Cell Free Translational Activity of Cardiac Cytoplasmic RNA", Symposium on Biology of Cardiac Overload. Eur. Heart J., 5(Supp), 225-229, (1984) prepared extracts from normal and experimental canine hearts in which a 100 mm Hg gradient was created across the ascending aorta for 6 hours. Experimental extracts were then treated (1) by ultrafiltration through YM 10 and YM 30 membranes,(2) by incubation with immobilized trypsin for 1 hour at 37.degree. C. and (3) by incubation in a boiling water bath for 10 minutes. Extracts were perfused through isolated rat hearts for 1 hour. Total cytoplasmic RNA was then extracted from the perfused heart and translated in a cell free medium containing [.sup.35 S]-methionine Incorporated label into newly synthesized protein was determined by liquid scintillation counting. A 13% mean increase in translational activity was produced by the fraction of the experimental extract passing through the YM 10 membrane compared with the material retained by YM 10 and YM 30 membranes. A 14% mean decrease in translational activity was observed in hearts perfused with experimental extracts treated with immobilized trypsin compared to untreated experimental extracts. There was no reported significant difference in translational activity of hearts perfused with experimental extracts subjected to boiling compared with non-boiled experimental extracts. The above data were said to suggest that the active moleules may be heat stable peptides or peptide containing substances of 10,000 daltons or less in molecular weight.
Hypertrophy represents the final visible result of a sequence of complex and precisely programmed events that are extremely difficult to unravel. To complicate the issue, the cardiac hypertrophy associated with pressure overload, (E. A. Breisch, F. C. White and B. M. Bloor, "Myocardial Characteristics of Pressure-overload Hypertrophy. A Structural and Functional Study", Lab. Invest., 51, 333-342, (1984)), volume overload, (P. Y. Hatt, K. Rakusan, P. Gastineau and M. Laplace, "Morphometry and Ultrastructure of Heart Hypertrophy Induced by Chronic Volume Overload (Aorta-caval Fistula in the Rat)", J. Mol. Cell. Cardiol., 11, 989-998, (1979)), exercise training, (P. Anversa, C. Beghi, V. Levicky, S. L. McDonald and Y. Kikkawa, "Morphometry of Right Ventricular Hypertrophy Induced by Strenous Exercise in Rat", Am. J. Physiol., 243, H856-H861, (1982)), ischemia, (F. Z. Meerson, "Development of Modern Components of the Mechanism of Cardiac Hypertrophy", Cir. Res., Suppl II, 35, 58, (1987)), and thyroxin administration (L. P. McCallaster and E. Page, "Effects of Thyroxin on Ultrastructure of Rat Myocardial Cells: A Stereological Study", J. Ultrastr. Res., 42, 136-155, (1973)), are all sligh;ly different, raising the possibility that there may be many molecular inducers of hypertrophy.
______________________________________ DEFINITIONS ______________________________________ Asp aspartic acid Asn asparagine Asx aspartic acid and/or asparagine Glu glutamic acid Glx glutamic acid and/or glutamine Ser serine Gly glycine Gln glutamine His histidine Arg arginine Thr threonine Ala alanine Pro proline Tyr tyrosine Val valine Met methionine Ile isoleucine Leu leucine Phe phenylalanine Lys lysine ______________________________________